1. Field of the Invention
This invention generally relates to an input device for use in inputting an instruction to a personal computer, and in particular, relates to an input device using a position detection signal of a movable object moving on a substrate.
2. Description of the Related Art
Conventionally, an input device, which inputs an instruction using position information of a movable object, is known. This input device is, for example, connected to a computer and is used as an input device to input an instruction of a user. Japanese Patent Application Publication No. 7-146102 (hereinafter referred to as Document 1) discloses an input device, in which a hall element is arranged at one end of a lower yoke and a movable object formed of a magnet and an upper yoke slides on the lower yoke. When the upper yoke is located on the hall element, the input device forms a closed magnetic circuit and detects the position of the movable object. In addition, an input device disclosed in Japanese Patent Application Publication No. 10-207616 (hereinafter referred to as Document 2) includes a reflecting plate provided on a movable object so that a user can place his or her finger to slide the movable object, a luminous element arranged below the reflecting plate, and a plurality of light receiving elements which receive lights emitted from the luminous elements and reflected on the reflecting plate. The input device detects the position of the movable object based on the detection signal of the receiving element.
There is a demand for reducing the size and the thickness of the input device mentioned above as in the case of the other electronics devices. However, the input device disclosed in Document 1 detects the position of the movable object by forming a closed magnetic circuit when the movable object approaches the hall element. For that purpose, the movable object has a build-up structure in which the upper yoke is secured on the magnet. The thickness of the input device increases if the movable object having the afore-mentioned structure is arranged in the input device. This does not satisfy the demand for reducing the thickness.
Further, when the upper yoke is used, the input device has an increased number of components and the input device grows in size. This does not satisfy the demand for reducing the size. In addition, the input device disclosed in Document 2 has a structure in which the luminous element is arranged below the reflect plate provided on the movable object and a light from the luminous element is reflected by the reflect plate. Therefore, it is necessary to provide a light path (space) between the reflect plate and the luminous element for reflection. This results in the increased thickness of the input device, and does not satisfy the demand for reducing the thickness.